Small Arpeggios
At the moment you cannot place arpeggios on grace notes. Additionally, arpeggios placed on small chords do not actually change in size themselves; to my knowledge there's no actual way to force "small" arpeggios: all arpeggio lines will remain the same size regardless of whether the note itself is smaller than the staff default.
If nothing else, an arpeggio on a small chord should be smaller than normal. Ideally, it should also be possible to put an arpeggio on a grace note, but right now I'll be content with smaller arpeggios so I can at least fake it.
Comments
See #307962: Can't add arpeggio to grace notes and #316283: Scale arpeggios attached to small notes
I would say making arpeggios on small chords (not notes) also small should definitely happen, that's just a bug fix really. I could also see someday adding a new feature where you can specify scaling for the individual symbols.
But arpeggios on grace notes - I'm struggling to imagine the real world use case for this that would make it worth the effort it takes to implement.
In reply to I would say making arpeggios… by Marc Sabatella
I ask by virtue of having encountered works where that is how it was written.
In hindsight the fact that I have a saved image of the example means I probably posted about this before, but ah well. For what it's worth, I did encounter this in another Medtner piece, so it isn't isolated to a single of his works. Is it common? No, and having the means to fake it would be perfectly sufficient. If nothing else, though, it is something that has been used in published works. Sure, there are other ways to notate this, but not necessarily in ways that are quite as succinct.
In reply to I ask by virtue of having… by LuuBluum
You did, see https://musescore.org/en/node/289306
In reply to You did, see https:/… by Jojo-Schmitz
Ah, that I did. Well, here's the other example I found, also Medtner: